1. Field of the Invention
This invention relates to a method of enhancing the activity of lysosomal .alpha.-Galactosidase A (.alpha.-Gal A) in mammalian cells and for treatment of glycosphingolipid storage diseases, in particular Fabry disease, by administration of 1-deoxy-galactonojirimycin and related compounds.
2. Background Information
Fabry disease (1) is a glycosphingolipid lysosomal storage disease caused by an X-linked inherited deficiency of lysosomal .alpha.-galactosidase A (.alpha.-Gal A), an enzyme responsible for the hydrolysis of terminal .alpha.-galactosyl residue from glycosphingolipids. A deficiency in the enzyme activity results in a progressive deposition of neutral glycosphingolipids, predominantly globotriaosylceramide (ceramide trihexoside, CTH), in vascular endothelial cells causing renal failure along with premature myocardial infarction and strokes in patients with this condition (2). This disorder is classified by clinical manifestations into two groups: a classic form with generalized vasculopathy and an atypical variant form, with clinical manifestations limited to heart. Recently, the atypical variant of the disease was found in 10% of adult male patients with unexplained left ventricular hypertrophy, increasing the estimation of frequency for the disorder (3), Like other glycosphingolipid lysosomal storage diseases, enzyme replacement therapy, gene therapy, bone marrow transplantation, and substrate deprivation are suggested as potential strategies for the treatment of this disease (4). However, at the moment the only treatment for this disorder is symptomatic management. Therefore, development of a new therapeutic strategy for this disease is urgently needed.
Studies (5) on residual .alpha.-Gal A activity of mutant enzymes revealed that some of mutant enzymes have similar kinetic properties to normal .alpha.-Gal A but with significant instability. This is considered as the case for most of atypical variant patients who generally showed higher residual .alpha.-Gal A activity than classical Fabry patients. For example (6), a purified mutant a-Gal A with a genotype of Q279E, found in a patient with atypical variant of Fabry disease, had the same Km and Vmax as the normal enzyme, but lost most of the enzyme activity by incubating the enzyme at pH 7.0 at 37.degree. C. for 30 min while the normal enzyme was stable under the same condition. Both mutant and normal enzymes were stable at pH 5.0 at 37.degree. C. Furthermore, the majority of the mutant enzyme protein in cells formed aggregate in endoplasmic reticulum (ER) and was quickly degraded (7), suggesting that the deficiency of the enzyme activity in this mutant maybe primarily caused by the unsuccessful exit of ER leading to excessive degradation of the enzyme protein. The present invention focuses on the aid of smooth escape of the enzyme from ER to prevent the degradation of the mutant enzyme.